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City: Roslyn Pa
What i do is scrape off the open winding with my fingernail. Use a heat gun clean up the area. Solder on the wire at the bottom of the winding Starting from the bottom wind the new turns in a cw direction. Solder on the top of the winding. Wire gauge is not very critical. RS probably has something that is close like 34 or 36g.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Thanks Terry.
The smallest my RS has is 30 gauge. Resistance is something like 100 ohm/ft vs 650 ohm/ft for 38. that might be stretching it a little, not sure. Everything I have found so far online, is like 1400 ft spools. Hate to buy that when I need less than 2' of wire. I'm also looking through some junk equipment for something like .004/.005/.006 diameter mag wire.
I'll continue looking.
-Brett
Posts: 15,818
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City: Jackson, NJ
Caperodder Wrote:Thanks Terry.
The smallest my RS has is 30 gauge. Resistance is something like 100 ohm/ft vs 650 ohm/ft for 38. that might be stretching it a little, not sure. Everything I have found so far online, is like 1400 ft spools. Hate to buy that when I need less than 2' of wire. I'm also looking through some junk equipment for something like .004/.005/.006 diameter mag wire.
I'll continue looking.
-Brett
Brett
(I am speaking as an EE, not as an experienced vintage radio repairman, so)
What's important here is not really the gage, but the diameter and the number of turns.
The inductance of the choke, when the winding diameter is much larger than the diameter (gauge) of the wire itself, is determined by the winding geometry.
And, considering that the current-bearing capability in this type coils is not very important (inlike in, say, power chokes or transformers), you have some freedom in choosing the wire gauge. Anything reasonably close to what you have (so it winds easily, and is not too flimsy, so you can solder it well) will probably do.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 47
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Joined: Oct 2011
City: West Barnstable, Massachu
Well, it's easy enough to try, just 4 winds. I'll go ahead with the 30 gauge and try it out.
Thanks,
-Brett
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Your welcome
The resistance isn't that important although 650 ohms a foot sounds very high for #38g. That winding is just for the coupling of the rf signal to the input grid of the mixer tube. It isn't in a frequency determining circuit. That would be the secondary of the coil.
I was a bit surprised to see that you had hv on grid 2 of the mixer tube (good), I was thinking that the oscillator wasn't operating. But it seems to be working ok.
Glad to help out when I can.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Well, I'm just a little disappointed. I have added the new coil winding, and all points on the coil measure correctly per the schematic. (.6 ohms between lugs 1 and 5) I wound the coil, exactly as I removed it, winding clockwise, (bottom facing), starting at the base.
Antenna clip to ground is now 32 Ohms. (was open prior to the coil repair)
All voltages on the 6A7 have remained the same.
The radio performs exactly as it did prior to surgery. Maybe two very faint signals, noise increasing as I climb the dial.
Going back to recheck wiring and new component values.
Any other thoughts?
-Brett
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Probably it's time to break out the signal generator and check out the IF and RF alignment.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
After reviewing your voltages I don't think your lo is running. The control grid of the 6A7 should read about -4v or so not +42. Recheck 10 and 11 for proper value and measure the resistance from pin 5 of 6A7 to the osc coil pin with the resistor on it. Should read a low resistance like 20ohms.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Hi Terry,
My apologies; pin 5 of the 6A7 is reading -42 volts. Didn't realize the meter swapped polarity. ® 10 was reading a little high, so I installed an new 47K resistor. © 11, I believe is an Aerovox Mica, (Orn-Brn-Orn) reading .001uf on my Fluke meter, but only comes into play when the Police band is switched on.
Between pin 5 of the 6A7 and lug 5 of the coil, I am getting like 45K Ohms, not a low 20 Ohms as you state.
Don't have an RF Generator, yet, but I'm keeping my eye out for one.
Regards,
-Brett
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Me thinks you got an open winding on the osc coil. Go head and pull it out. Inspect for green spots (rot) and check each winding with and ohm meter. All windings should read a low resistance like less than 10 or 20 ohms.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Hi Terry,
Let me first tell you how much I appreciate this help.
This is what I am measuring while the oscillating coil is still in the radio, switch set to BC. I've included a picture just in case I am not reading the schematic correctly.
Reading from the bottom, clockwise. (not counting the ground lug)
Lug 1 to Lug 4 - .6 Ohms
Lug 5 to top of coil - .6 Ohms (then proceeds to 6A7 pin 5)
Lug 2 to Lug 3 - 3.8 Ohms
Lug 4 to Lug 5 - 2 Ohms
No signs of any green or other corrosion.
-Brett
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
>and measure the resistance from pin 5 of 6A7 to the osc coil pin with the resistor on it. >Should read a low resistance like 20ohms.
Ok something isn't correct. What I had you do was measure across the total primary of the osc coil on the above post.
You said it was 45,000 ohms. This is way too high.
When I look at your drawing all of the resistances look low.
What's up?
Add numbers to the pic doesn't tell me anything as my diagram doesn't have these notation.
Does yours?
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Hello Terry,
Sorry for not sending a corresponding schematic with my pin numbers. (now included) I must have been reading the incorrect pins when I read the 45k.
One side of the coil should read 3.4 Ohms per schematic (my lugs 2 and 3). I'm getting 3.8 Ohms.
The other side of the coil, going through all of the windings on the schematic are .3, 1.6 and .5 (2.4 Ohms total) I'm reading (my lug 1, with the 51K resistor) and the top of the coil which goes to pin 5 on the 6A7), is 2.6 Ohms.
Forgive my amateur experience, but I don't understand where the 20 Ohms comes from.
-Brett
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
The 20 ohms was just a guess on my behalf without looking or perhaps forgetting what I saw.
Lets measure from oscillator section of the tuning at the connection on the side to chassis ground. You might want to replace 13 the 110 mmfd mica cap
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 47
Threads: 5
Joined: Oct 2011
City: West Barnstable, Massachu
Hi Terry,
Not sure I understand the point you refer to.
"Lets measure from oscillator section of the tuning at the connection on the side, to chassis ground"
I've also gone ahead and replaced 13 with a 100pf cap. Also rechecked 14's resistance. No change.
-Brett
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